letro aside from being an ai, also increases l.h., the reason you may want to run a serm is due to the body increasing production of the aromatase enzyme due to the letro and when you cease using the letro, you will have an exsessive amount (rebound) of the aromatse enzyme to readily aromatize the test (increased not only from lack of t aromatizing into E, but also do to the increased produciton of l.h.) into E.
all in all, it's a big hormonal imbalencing act you most likely dont want to get started, it would be easier to use a fat burner of some type and hard work in the gym, rather than juggle your hpta all over the place.